1. Field of the Invention
The present invention relates to seat reclining mechanisms for adjusting a tilt angle of a seat back of a vehicle seat. More particularly, the present invention relates to seat reclining mechanisms that are disposed on one side of the vehicle seat
2. Description of the Related Art
Typically, a known seat reclining mechanism for adjusting a tilt angle of a seat back of a vehicle seat includes a pair of opposing disk-like housings, i.e., a first housing and a second housing. The first housing is affixed to a cushion frame that supports a vehicle seat cushion. The second housing is affixed to a seat back frame that supports the vehicle seat back. The first and second housings are circumferentially connected by a fastener or clip ring so that the second housing can move or rotate relative to the first housing around a rotational axis. Further, the rotational axis corresponds to a common centerline of the first and second housings.
The seat reclining mechanism also includes a rotational rod or shaft that extends along the rotational axis through the cushion frame and the seat back frame, as well as through the first and second housings. The rotational shaft includes an extended portion (manipulating portion), which portion is typically connected to a seat operation handle or lever.
The seat reclining mechanism further includes a locking means that can prevent the second housing from rotating relative to the first housing, thereby locking the seat reclining mechanism. The locking means essentially consists of a hinge cam, a slide member and a pair of pawls that are received within the housings. The hinge cam is secured to or integrally formed with the rotational shaft, so as to rotate with the rotational shaft. The slide member is laterally movably or slidably attached to the first housing. The slide member includes a specially shaped central bore that receives the hinge cam. The central bore partially engages the hinge cam, so that the slide member can laterally slide or move when the rotational shaft rotates. As will be recognized, the slide member is configured in order to reliably prevent the slide member from rotating relative to the first housing.
In addition, the first housing is formed with a pair of vertical guide grooves, which grooves are positioned on respective sides of the slide member. The pawls are vertically movably or slidably received within the guide grooves of the first housing. The pair of pawls are configured to engage the slide member. Thus, the pawls can vertically slide or shift when the slide member laterally slides. As will be recognized, because the pawls are received in the guide grooves of the first housing, the pawls are prevented from rotating relative to the first housing.
Further, the second housing has an inner circular surface. A pair of concave toothed portions circumferentially extend over two separate portions of the inner circular surface. Each of the pawls has a curved outer surface. A corresponding convex toothed portion is provided on each pawl for releasably engaging the respective concave toothed portions of the second housing.
In addition, a biasing (spiral) spring is disposed within the first housing. The spiral spring urges (biases) the rotational shaft in a counterclockwise direction. As a result, the rotational shaft is normally retained in a locked position. When the rotational shaft is retained in the locked position, the slide member is positioned at the leftmost position. When the slide member is retained in this position, the slide member pushes or urges the respective pawls in opposite outward directions so that the respective convex toothed portions of the pawls engage the concave toothed portions of the second housing. In this state, the second housing is prevented from rotating relative to the first housing, thereby locking the seat reclining mechanism. As a result, the seat back frame is locked in position relative to the cushion frame and thus, the seat back is locked relative to the seat cushion.
As described above, because the pawls are received in the guide grooves of the first housing, the pawls are prevented from rotating relative to the first housing. Therefore, when the respective convex toothed portions of the pawls engage the concave toothed portions of the second housing, the second housing is prevented from rotating relative to the first housing, thereby locking the seat reclining mechanism. However, considerable clearances are defined between the pawls and the guide grooves such that the pawls are easily assembled to the first housing. Such clearances allow the pawls to idly laterally move within the guide grooves. As a result, the second housing can be rotated relative to the first housing by a small degree when the seat reclining mechanism is locked. Such rotation of the second housing relative to the first housing may cause backlash between the cushion frame and the seat back frame when the seat reclining mechanism is locked.
A method for eliminating such backlash is taught, for example, by U.S. Pat. No. 6,220,666, in which after the pawls are received within the guide grooves, the first housing is partly deformed at portions adjacent to the guide grooves by a punch press, thereby forming projections that project into the guide grooves by a desired projecting distance. The projections thus formed may slidably contact the pawls, so that the pawls can be prevented from laterally moving within the guide grooves. Thus, the second housing is prevented from rotating relative to the first housing when the seat reclining mechanism is locked. As a result, the backlash between the cushion frame and the seat back frame can be eliminated when the seat reclining mechanism is locked.
However, it is very difficult to precisely control deformation of the first housing (projecting distances of the projections) by the punch press. That is, the first housing can be excessively deformed. Therefore, it is possible that the pawls cannot move or slide within the guide grooves.
It is, accordingly, one object of the present teachings to provide improved seat reclining mechanisms.
For example, in-one aspect of the present teachings, a seat reclining mechanism for a vehicle seat may include a first housing having a guide groove, a second housing having a toothed portion, and a pawl slidably received in the guide groove. The guide groove has first and second guide surfaces. The pawl has first and second side surfaces that respectively correspond to the first and second guide surfaces of the guide groove. The pawl engages the toothed portion of the second housing by sliding from its non-engaging position to its engaging position along the guide groove, thereby preventing the second housing from rotating relative to the first housing. The first side surface of the pawl and the first guide surface of the guide groove are arranged and constructed such that a clearance defined therebetween is changed so as to have an optimal width when the pawl is shifted from the non-engaging position to the engaging position.
Thus, when the pawl is shifted from the non-engaging position to the engaging position, the clearance defined between the first side surface of the pawl and the first guide surface of the guide groove is effectively changed so as to have the optimal width. Therefore, the pawl is prevented from laterally moving within the guide groove when the pawl is positioned in the engaging position (i.e., when the seat reclining mechanism is locked). Thus, the second housing is effectively prevented from rotating relative to the first housing when the pawl is positioned in the engaging position. As a result, backlash between a cushion frame and a seat back frame that are linked by the seat reclining mechanism can be effectively eliminated or minimized when the seat reclining mechanism is locked.
Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.